1. Field of the Invention
The present invention relates to a thin film magnetic head and fabrication process therefor. More specifically, the invention relates to a thin film magnetic head to be employed in a magnetic recording apparatus, such as a magnetic disk apparatus.
2. Description of the Related Art
Conventionally, in such kind of thin film magnetic head, a protective film 12, a lower shield 13, a reading MR (magnetic resistor) 14, a common pole (lower magnetic body) 15, an insulation film, a photoresist layer 17 and a coil 18 are formed on a substrate 11 in sequential order, a light is irradiated on the photoresist layer 17 via a mask 19 (see FIG. 5A) to perform patterning of the photoresist layer 17, as shown in FIG. 5.
After patterning of the photoresist layer 17, heat treatment is performed for hard-baked the photoresist layer (interlayer insulation layer) 20 (see FIG. 5B), and the upper magnetic body 10 and a protective layer are formed thereon. The interlayer insulation layer 20 is intended to provide insulation between the conductor coils or between the magnetic layer and the conductor coil and also to reduce step height of the magnetic layer and the conductor coil.
Here, as shown in "PHOTORESIST FOR USE IN SILICON ETCHING BATHS" (IBM Technical Disclosure Bulletin Vol. 14, No. 8, p. 2309, 1972), for example, there is a method to employ a positive type photoresist of novolac resin type as an insulation layer.
In this case, after applying a positive type photoresist over the entire surface by way of a spin coating method or so forth, an ultraviolet ray is irradiated except for the portion to be left as an insulation layer and development is performed with an alkali aqueous solution to form a pattern of the insulation layer (see FIG. 5A).
The photoresist pattern of the insulation layer is required to be stably present even after the subsequent processes, baking is effected at a temperature higher than or equal to 250.degree. C. to form the interlayer insulation layer 20 (see FIG. 5B).
On the organic insulation layer, the upper magnetic core layer is formed. The protective layer is formed thereover by way of sputtering (see FIG. 5B) to complete the thin film composite magnetic head. Concerning the fabrication process, there is a technology disclosed, for example, in Japanese Unexamined Patent Publication (Kokai) No. Heisei 2-254615.
In the conventional fabrication process of the thin film magnetic head as set forth above, for a baking temperature higher than or equal to 250.degree. C. of the hard-baked photoresist, stability against heat is required for material forming the respective head. However, in the spin valve head material attracting attention as a high density MR head material, stability against such temperature is not always sufficient.
Therefore, it is required to develop a process that can be performed at lower temperature. However, the positive type novolac resin is low in thermal stability and has a low softening point. Therefore, a high temperature baking process has to be provided in order to attain stability at high temperature.
On the other hand, an apex in the direction of section of the interlayer insulation layer has to be optimized in view of recording characteristics. Conventionally, the apex is set on the basis of the heat treatment condition and viscosity of the resist material, and thus width in selection is narrow and setting of the process is difficult.